A digital audio disk oriented for use in only reproduction is commercialized as a so-called "compact disk" (hereinafter referred to as "CD") and a development of those capable of conducting rewriting of information is advancing. As a rewritable optical disk, there is one which utilizes opto-magnetic effect. This disk utilizes in the recording the nature of material that when the material is heated up to above Curie temperature by such as laser light, the coercive force becomes almost zero and the magnetization can be inverted by a small external magnetic field, and utilizes in the reproduction the nature of material arising Kerr effect in which the polarization plane of incident laser light is rotated by the direction of magnetization.
As another rewritable optical disk, those utilizing the change in phase between crystal phase and non-crystal phase is known.
By the way, in conducting recording or editing in such as a music studio, it is quite rare that all performers gather with together and conduct performances for recording at the same time. Generally, in such case, firstly recording of part of rhythm section such as drums is conducted, thereafter recording of part of melody section is conducted, and finally recording of part of chorus section is conducted, thereby completing a tune. Then, the performance of the respective part is conducted with listening to the performances of the other parts which are recorded prior. Accordingly, an apparatus for conducting recording and editing in such as a music studio, has to be provided with a function of recording new information with multiplying the same on the previously recorded information along with reproducing the previously recorded information.
A prior art optical information recording and reproducing apparatus provided with such a function is disclosed in Japanese Laid-open Patent Publication No. 63-306536.
FIG. 2 shows a state where a desired track in information recording material is irradiated by a light beam sequence and FIG. 3 shows a functional diagram for explaining the recording and reproducing operation.
In these figures, a laser beam 14 as a first light beam exhibits a function of reproducing information which is already recorded in a disk as an information recording material. A laser beam 15 as a second light beam exhibits a function of recording new information on the information recording material. A laser beam 16 as a third light beam exhibits a function of erasing information which is reproduced by the first light beam 14. These three kinds of light beams are arranged on a predetermined track 21 in the order of first, third, and second light beams 14, 16, and 15 along the advancing direction of disk A. Furthermore, noticing a predetermined position of the disk, the time interval from timing when the first light beam 14 is irradiated to timing when the second light beam 15 is irradiated is t.sub.H.
In FIG. 3, driving means for driving the disk as information recording material, an optical system for guiding light beam, detection means for detecting a reproduced signal or control signals, and servo-control means may be constituted by known devices and they are not shown here for simplification.
A reproduced signal 41 reproduced by the first light beam 14 is subjected to deinterleaving processing and error correction decoding processing by the decoder circuit 42. The reproduced signal subjected to such processing is mixed with an external signal 44 which is applied from the outside in the mixing circuit 40. Thereafter, the signal subjected to this mixing processing is subjected to coding processing and interleaving processing in the encoder circuit 48, and the signal is rerecorded on the disk as a new recording signal 49 by the second light beam 15. Then, if it is supposed that the required time for the processing at the decoder circuit 42 is t.sub.1 and the required time for the processing at the encoder circuit 48 is t.sub.2, the time interval t.sub.H between the operation timing of the first light beam 14 and the operation timing of the second light beam 15 may be set as in the following. EQU t.sub.H .gtoreq.t.sub.1 +t.sub.2
Furthermore, because the third light beam for erasing 16 is located between the first light beam 14 and the second light beam 15, the recording information at a predetermined position of the disk 2 has already been erased when a new recorded signal 49 is to be recorded.
The manner of operation of the prior art device will be described in detail.
The mixing circuit 40 is constituted by a first attenuator 43 for attenuating the decoded reproduced signal 41, a second attenuator 45 for attenuating an external signal 44 which is newly added from the outside, and an adder 46 for adding the output signals from the first and second attenuators 43 and 45. Herein, the attenuation quantity of the first attenuator 43 and the attenuation quantity of the second attenuator 45 are adjusted to vary complementarily with each other, that is, with holding a relation therebetween.
For example, in recording information to a new disk, if it is supposed that the attenuation quantity of the first attenuator 43 is made maximum and the attenuation quantity of the second attenuator 45 is made zero, as a result of the addition by the adder 46, only the external signal 44 appears at the output of the adder 46 and this is subjected to an encoding processing by the encoder circuit 48 and the output thereof is recorded by the second light beam 15.
Next, to thus recorded information, another external signal can be newly added. In such case, in a state where the attenuation quantity of the first attenuator 43 is made zero and the attenuation quantity of the second attenuator 45 is made maximum, the reproduction operation is started. Then, the reproduced signal 41 is subjected to an error correction processing by the decoder circuit 42, and it is subjected to an encoding processing by the encoder circuit 48 as it is, and it is recorded to the original position on the disk by the second light beam 15. Then, by changing the attenuation quantity of the first and second attenuators 43 and 45 properly at the timing when the external signal 44 is to be recorded additionally, a signal which is obtained by mixing the reproduced signal 41 from the disk and the external signal 44 at a desired ratio is output at the output of the adder 46. Then, by properly adjusting the changing speeds of the attenuation quantity of the first and second attenuators 43 and 45, a desired cross-fade property (one of the two inputs is faded-in and the other is faded-out) is obtained. Herein, the above described mixing state can be confirmed by the monitor output 47.
In the prior art optical information recording and reproducing apparatus of such a construction, three light beams are required for recording, reproduction, and erasing of information. Accordingly, these three light beams have to be controlled in their position determination accurately onto the same track on the disk, and thus the circuits required therefor increase and accompanying therewith the reliability of the apparatus itself is lowered. Furthermore, the optical head for generating the light beam is of high cost, and the increase in the number of light beams leads to an increase in the production cost of the apparatus itself, thereby resulting in an obstruction in the production thereof.
Another prior art will be described as follows.
In an opto-magnetic disk, there is a magnetic field modulation system as a method of recording new information into a disk which has already recorded information. In this system, while continuously irradiating laser light to the opto-magnetic disk thereby to heat the recording material up to above Curie temperature to erase the information, a magnetic field is applied to the opto-magnetic disk by the magnetic field applying head with making the polarity of the magnetic field, that is, N or S in accordance with the information "1" or "0" of the writing-in information, whereby a new writing-in bit is recorded in an instance when the recording material is cooled down to below Curie temperature.
An idea of obtaining a rewritable digital audio disk apparatus for recording and reproducing audio signals in CD format using this system is proposed in such as Technical Search Report MR 87-37 of Japanese Society of Electronics, Information, and Communication Engineers.
The fundamental construction of a rewritable digital audio disk apparatus utilizing a magnetic field modulation system will be described with reference to FIG. 6.
In FIG. 6, reference numeral 1 designates an opto-magnetic disk which records information in accordance with the magnetization direction. An optical head 2 is provided to reproduce or erase information recorded in the opto-magnetic disk 1. A light beam comprising laser light 3 emitted from the optical head 2 is irradiated to the opto-magnetic disk 1 through an objective lens actuator 4. This actuator 4 is provided to adjust the focus and position of the light beam 3 emitted from the optical head 2 so that the light beam 3 is correctly irradiated to the opto-magnetic disk 1. An analogue digital converter 5 (hereinafter referred to as "A/D converter") is provided to convert an input audio signal to a 16 bit parallel digital signal. A CD encoder 6 is provided to conduct conversion of digital signal from the A/D converter 5 to a signal which can be recorded into the opto-magnetic disk 1 as a signal equivalent to CD format signal. A magnetic field applying head 7 is provided to apply a magnetic field in a direction in accordance with the signal from the CD encoder 6 thereby to record the signal. A CD decoder 8 is provided to convert the signal reproduced from the optical head 2 to a 16 bit parallel digital signal. A digital to analogue converter (hereinafter referred to as "D/A converter") is provided to convert the digital signal from the CD decoder 8 to an audio signal.
The device will operate as follows. Herein, it is supposed that a tracking guide groove is etched in the opto-magnetic disk 1.
First of all, in the recording, the optical head 2 is moved to a position where information is to be recorded and the light beam 3 is correctly irradiated to the opto-magnetic disk 1 with focused and correctly positioned by the objective lens actuator 4. Next, an audio signal to be recorded is input to the A/D converter 5. The signal input to the A/D converter 5 is converted into a digital signal and this digital signal is encoded by the CD encoder 6 to be supplied to the magnetic field applying head 7 as a signal equivalent to CD format signal. The magnetic field applying head 7 applies an external magnetic field to the opto-magnetic disk 1 with making the polarity of the magnetic field, that is, N or S in accordance with the signal from the CD encoder 6. At the same time, the intensity of the light beam 3 from the optical head 2 is increased and thus the recording is started.
When the recording is to be stopped, the intensity of the light beam 3 is lowered, and a signal is stopped to be applied to the magnetic field applying head 7, whereby the generation of a magnetic field is halted.
When the reproduction is to be conducted, the optical head 2 is moved to the position of the recorded information, and similarly as in the recording, the light beam 3 is projected onto the opto-magnetic disk 1 by the function of the objective lens actuator 4 so as to adjust the focus and the track position, and the signal is reproduced from the optical head 2. The reproduced signal is sent out to the CD decoder 8 and is converted into a 16 bit parallel digital signal, and finally, an audio signal is obtained at the output of the D/A converter 9.
Next, the operation in a case where a new signal is to be written in into a disk which has already recorded information will be described.
In such case, the rewriting of a new signal is conducted from a point in the way of the original signal as shown in FIG. 7. First of all, the output signal is monitored in the reproduction state, and the reproduction is conducted to a required position, whereby the optical head 2 is moved to a position where the rewriting is to be conducted. Next, a signal to be recorded is input and this signal is sent to the magnetic field applying head 7 and a magnetic field is generated in accordance therewith. At the same time, the intensity of the light beam 3 is increased and the recording is started. Thus, the rewriting operation is conducted.
The recording and reproduction are conducted as described above in this second prior art device. When only a portion is to be rewritten or a signal is to be inserted into only a portion, especially when only the conclusion point of the portion to be rewritten is clear and the portion beyond the conclusion point is to be remained in such prior art device, there is a problem in that the position of the conclusion point is difficult to be precisely determined although the starting point of the rewriting may be arbitrary to some degree. Therefore, there may be a possibility that required data would be erroneously deleted.
As a method of solving this problem, it is conceived to provide another optical head prior to the presently existing optical head 2 and to control the recording by the behind optical head 2 with confirming the reproduced signal before rewriting by the prior optical head 2. However, this method requires a construction capable of moving two optical systems correctly onto the same track on the disk, thereby resulting in problems in view of cost and reliability.